SOERENSEN ORLA LANG (DK)
CHRISTENSEN FLEMMING LAUSEN (DK)
SOERENSEN ORLA LANG (DK)
GB969090A | 1964-09-09 | |||
US4211617A | 1980-07-08 | |||
US3403082A | 1968-09-24 | |||
US5939011A | 1999-08-17 | |||
US3649474A | 1972-03-14 |
1. | A method of forming a mandrel having a shaped plating surface for receiving buildup of plating metal deposited thereon by electrodeposition, which method comprises: providing a solid model body having a shaped surface which is a negative image of the plating surface of the desired mandrel, if not already so activated, activating the shaped surface of the model body to receive buildup of copper in a copper electrodeposition bath operating at a temperature below 30°C, electrodepositing a layer of copper on the shaped surface of the model body in said bath, casting a backing mass directly or indirectly against the exposed surface of the copper layer on the model body causing the backing mass to solidify and bond to the copper layer, separating the backing mass together with its bonded copper layer from the surface of the model body, and optionally working the then exposed surface of the copper layer, the resultant backing mass and bonded copper layer constituting the desired mandrel, the exposed surface of the copper layer being the desired shaped plating surface. |
2. | A method as claimed in claim 1 wherein the shaped surface of the model body includes grooves which create ridges on the plating surface of the copper layer, which ridges are adapted for masking to prevent electrodeposition of plating metal thereon during subsequent use of the mandrel for electrodeposition thereon of a plated metal shell. |
3. | A method as claimed in claim 1 or claim 2 wherein the shaped surface of the model body is activated for copper electrodeposition by applying thereto a coating containing silver. |
4. | A method as claimed in any of the preceding claims wherein a second solid model body having an electrodeposited copper layer is formed in the same manner as the first, and the first and second model bodies are arranged in a desired spaced relationship with opposed copper layers, and the backing mass is cast between the spaced model bodies such that when solidified it bonds to both copper layers before separation from each model body, the resultant backing mass and bonded copper layers constituting the desired mandrel, the exposed surfaces of the copper layers being the desired shaped plating surfaces. |
5. | A method as claimed in claim 4 wherein the model bodies are maintained in spaced relationship by spacing posts extending between their respective copper surfaces. |
6. | A method as claimed in any of claims 1 to 5 wherein an adhesive is applied to, or keying elements are fixed to, the copper layer (s) of the model body (ies) whereby when the backing mass is cast against the copper layer (s) it becomes adhesive bonded to, or becomes keyed into, the solidified backing mass. |
7. | A method as claimed in any of claims 1 to 6 wherein the backing mass is cast indirectly against the copper layer (s) of the model body (ies) via an intermediate body or layer which increases the rigidity and/or strength of the bond between copper layer and solidified backing mass relative to the rigidity and/or strength of the bond achieved in the absence of such intermediate body or layer. |
8. | A method as claimed in any of the preceding claims comprising the additional step of electrodepositing a layer of gloss nickel on the copper layer (s). |
9. | A method as claimed in claim 8 wherein the layer of gloss nickel is treated with a separation assisting agent such as albumin, and a shell of plating metal is electrodeposited on the gloss nickel layer, the separation agent aiding separation of the electrodeposited shell of plating metal from the bright nickel layer. |
10. | A method as claimed in claim 9 wherein the plating metal is nickel or a nickelcobalt alloy. |
11. | A method as claimed in any of the preceding claims wherein the model body is of foamed or unfoamed plastics, wood, laminated wood, metal alloy or ceramic material. |
12. | A method as claimed in claim 11 wherein the model is of foamed polyurethane. |
13. | A mandrel having a plating surface for receiving buildup of plating metal deposited thereon by electrodeposition, which mandrel comprises a shaped layer in the form of an electrodeposited copper shell, one surface of which is bonded directly or indirectly to a backing mass, the other surface being exposed and constituting the mandrel's plating surface. |
14. | Electrodeposition apparatus including an anode body comprising plating metal, a cathode body having at least one exposed surface region for receiving buildup of plating metal by electrodeposition, an electrolyte solution comprising a salt of the plating metal, and means for passing current between the anode and cathode bodies via the electrolyte solution, CHARACTERISED IN THAT the cathode body comprises at least one shaped layer in the form of a copper shell one surface of which is bonded directly or indirectly to a backing mass, the other surface being at least partly exposed to the electrolyte solution, such exposed region (s) constituting the surface region (s) for receiving build up of plating metal. |
15. | A method as claimed in any of claims 1 to 12, a mandrel as claimed in claim 13, or apparatus as claimed in claim 14, wherein the backing mass is a ceramic. |
16. | A method, mandrel or apparatus as claimed in claim 15, wherein the ceramic is a chemically bonded ceramic. |
17. | A method, mandrel or apparatus as claimed. in claim 16 wherein the chemically bonded ceramic is a cementbased paste, mortar or concrete. |
18. | A method, mandrel or apparatus as claimed in claim 17 wherein the chemically bonded ceramic is a lightweight or low shrinkage concrete. |
19. | A method as claimed in any of claims 1 to 12, a mandrel as claimed in claim 13, or apparatus as claimed in claim 14, wherein the backing mass is or comprises a DSP material. |
20. | A method, mandrel or apparatus as claimed in claim 19 wherein the DSP material is a cement based mortar or concrete. |
21. | A method, mandrel or apparatus as claimed in claim 20 wherein the DSP material is reinforced with steel fibres. |
22. | A method as claimed in any of claims 1 to 12, a mandrel as claimed in claim 13, or apparatus as claimed in claim 14, wherein the backing mass is an aggregatecontaining resin matrix. |
23. | A method, mandrel or apparatus as claimed in claim 22 wherein the resin matrix is of polyurethane, acrylic, polyester or epoxy resin. |
24. | A method as claimed in any of claims 1 to 12, a mandrel as claimed in claim 13, or apparatus as claimed in claim 14, wherein the backing mass is a metal alloy. |
Background to the Invention In electrodeposition processes, for example electroplating or electroforming processes, a plating metal is deposited on an electrically conductive shaped surface of a body, often known as a"mandrel". If the material of which the body of the mandrel is constructed is itself non-conductive, the deposition surface may be rendered conductive by applying a thin conductive coating, for example of silver-based paint, or chemically reduced silver or copper In practice, the choice of mandrel material is often limited. For example, a monolithic mandrel must be constructed from a material which can be surface shaped, for example by casting or milling, to the required tolerances of the desired shaped plating surface. The mandrel material should also be resistant to acid or chemical degradation under the conditions of the electrodeposition process. Furthermore, especially for electroforming large surface area metal shells, the mandrel as a whole must be self-supporting and substantially non- deformable under the electrodeposition conditions, otherwise there will be a risk of deformities and/or internal stresses in the deposited metal shell. In the latter connection it is undesirable to construct the mandrel of a material which has a coefficient of thermal expansion (CTE) greatly different from that of the plating metal (which is typically about 13-14 lim per m per °C (Lm-m-l-OC-1)), since the
different thermal expansion characteristics of the mandrel and plating layer during a heat-generating deposition process may also lead to undesirable deformities and/or internal stresses in the plated shell. Materials which are capable of being milled or cast for the desired plating surface shape do not in general have the required CTE properties.
This invention makes available a method for constructing a stable composite mandrel comprising a copper layer as plating surface, bonded to a thermally stable backing mass having the desired self-supporting, substantially non- deformable, acid and chemical resistant, and acceptable CTE properties. The resultant mandrel is useful in electrodeposition apparatus, for example for the construction of tools for forming sheet metal or plastics parts.
Description of the Invention The present invention provides a method of forming a mandrel having a shaped plating surface for receiving build-up of plating metal deposited thereon by electrodeposition, which method comprises: providing a solid model body having a shaped surface which is a negative image of the plating surface of the desired mandrel, if not already so activated, activating the shaped surface of the model body to receive build-up of copper in a copper electrodeposition bath operating at a temperature below 30°C, electrodepositing a layer of copper on the shaped surface of the model body, casting a backing mass directly or indirectly against the exposed surface of the copper layer on the model body
causing the backing mass to solidify and bond to the copper layer, separating the backing mass together with its bonded copper layer from the surface of the model body, and optionally working, for example by milling, grinding, polishing, etching or machining, the then exposed surface of the copper layer, the resultant backing mass and bonded copper layer constituting the desired mandrel, the exposed surface of the copper layer being the desired shaped plating surface.
The first step is to provide a solid model body having a shaped surface which is a negative image of the plating surface of the desired mandrel. The model may in principle be made of any solid material the surface of which may be shaped to the desired tolerances, such as wood including laminated wood, foamed or unfoamed plastics, metal or metal alloy, ceramic materials, wax or clay. In particular, as discussed below, the model material may be chosen without regard to its CTE. However, polyurethane foam will often be the preferred material, since it is cheap and highly amenable to shaping using standard CAD ("computer aided design") software and hardware. In this case however, the surface of the model may be crumbly or otherwise unstable, and it may be preferred to stabilise the surface for milling or for copper deposition. For example, the surface of the foamed polyurethane model may be shaped as desired, with the tolerances of the shaping being chosen to accommodate a thin resin impregnated fibrous non woven mat applied to and conforming to the shaped surface. That resin impregnated mat may then be milled or otherwise worked to the desired tolerances for copper deposition. The worked resin impregnated mat provides a more stable surface for copper deposition than a directly milled foamed polyurethane surface.
If the material from which the model is constructed is not electrically conductive, or for other reasons the shaped surface of the model is not electrically conductive, the next step is to activate that surface for deposition of copper in an electrodeposition bath. This may be done in conventional manner by spraying an electrically conductive coating, for example of silver-based paint, onto the surface, or by forming a conductive layer of chemically reduced silver or copper thereon.
It is a feature of the present invention that the copper layer may be deposited on the shaped surface of the model in a"cold"electrodeposition bath, ie one which operates at a temperature below about 30°C, for example in the range 15°C to 25°C. Thus, the thermal expansion properties of the material from which the model is constructed are not critical, and in particular need not be matched to those of the copper layer. Because the deposition temperature is low, the copper layer may be deposited without the distortion which would be expected if a different plating metal requiring a high temperature bath were used with a model material having non-matched CTE.
The thickness of the copper layer deposited is not critical. A layer of from 10 to 50 microns will normally be satisfactory. Economic considerations will normally rule out the use of thicker layers, but they are not excluded from use in the present invention on functional grounds.
After deposition of the copper layer on the shaped surface of the model, the next step is to cast a suitable backing mass against the exposed face of the copper layer on the model. The castable backing mass may be of any material compatible with the copper layer.
A strong bond between the backing mass and the copper layer is desirable, since the backed copper layer is to be separated from the model body to form the stable mandrel for use in the fabrication of electrodeposited metal shells. In the
event that a direct bond between the copper layer and the backing mass is insufficiently strong and/or rigid, the backing mass may be cast indirectly against the copper via an adhesive layer, or intermediate body or layer which increases the rigidity and/or strength of the bond between copper and solidified backing mass relative to the rigidity and/or strength of the bond achieved in the absence of such intermediate body or layer. For example, the surface of the copper layer against which the backing mass is to be cast may be primed with an epoxy resin glue, a non woven mat of fibrous material may be applied to the primed surface, and the non woven mat may be impregnated with a paste of resin filled with particulate material such as sand or aluminium grains. The resultant impregnated mat provides a rough surface to which the cast backing material is effectively keyed. Alternatively, prior to casting the backing mass, keying elements such as studs or aggregate chips may be formed on or fixed (for example by gluing) to the non-plating face of the copper layer, whereby when the backing mass is cast directly or indirectly against that face the copper layer becomes keyed into the backing mass.
Examples of castable backing masses include metals and metal alloys, concrete or mortar, DSP materials, (DSP: Densified Systems containing ultrafine Particles) and aggregate-filled polyurethane, acrylic, polyester or epoxy resins.
DSP materials are particularly useful, that is materials based on densely packed particle systems with ultrafine particles homogeneously distributed between the densely packed fine particles by means of an effective dispersing agent, these materials typically being fibre-reinforced. Examples of such materials are disclosed, e. g. , in US Patents Nos. 5,234, 754 and 4,588, 443. (It may be noted that US Patent No. 4,923, 665 discloses the application of a metal coating on DSP materials, e. g. by casting DSP materials against a metal layer such as a nickel layer formed by electrodeposition, and that International Patent Application publication No. WO 82/01674 relates to a shaping tool made in this manner. ) A type of DSP material which has been found suitable for the purpose of the invention is a mortar having a cement-based matrix, the cement particles
constituting the densely packed fine particles, the ultrafine particles being silica fume particles, the dense and homogeneous structure having been obtained using an effective amount of a concrete superplasticizer, the mortar preferably being reinforced with fibres such as plastics or steel fibres.
After cast backing mass has solidified, the next step is to separate the backing mass together with its bonded copper layer from the surface of the model body.
This will not normally present difficulty, particularly if the surface of the model has been coated with silver to activate it for copper deposition. Sometimes however, separation may result in remnants of the detached model, or of the silver layer, adhering to the now exposed face of the copper layer. In such cases, the exposed copper surface may need to be worked, for example by milling, grinding, polishing, etching or machining, to remove such remnants or otherwise improve the quality of the copper layer for subsequent processing.
The resultant backing mass and bonded copper layer constitutes the desired composite mandrel, the exposed surface of the copper layer being its desired shaped plating surface. This mandrel forms another aspect of the invention.
Since the copper layer has been deposited in a"cold"electrodeposition bath, it is substantially free of distortions and internal strains which might have been introduced by unmatched thermal expansion properties of the model on which it was formed. Furthermore, because the backing mass was cast against the copper layer while the latter was still stably supported by the model, no substantial distortions are introduced by the casting process. The plating surface of the composite mandrel is thus a faithful inverse image of the original shaped surface of the model. Additionally, the copper plating surface is securely bonded to a stable backing mass, and is thus suitable for use in electrodeposition processes where higher bath temperatures make thermal stability of the plating surface of the mandrel critical.
As stated, the end product of the method of the invention is a composite mandrel for use in an electrodeposition process. The method of the invention is applicable to the preparation of mandrels having two plating surfaces. In such cases, a second solid model body having an electrodeposited copper layer is formed in the same manner as the first, and the first and second model bodies are arranged in a desired spaced relationship with opposed copper layers, and the backing mass is cast between the spaced model bodies such that when solidified it bonds to both copper layers before separation from each model body, the resultant backing mass and bonded copper layers constituting the desired mandrel, the exposed surfaces of the copper layers being the desired shaped plating surfaces.
The models may be maintained in spaced relationship by spacing posts extending between their opposed copper faces, these posts becoming subsumed into the cast backing mass.
The eventual utility of mandrels according to the invention is in electrodeposition processes, in particular in the electrodeposition of plating metals such as nickel or nickel-cobalt alloy shells from nickel chloride baths, for use as pressing tools.
For such uses, it is often desirable to electrodeposit a layer of bright nickel on the copper plating surface of the mandrel, prior to the deposition of the final plating metal shell. In such cases the layer of gloss nickel is preferably treated with a separation assisting agent such as albumin, prior to depositing the final plating metal shell, the separation agent aiding separation of the electrodeposited shell of plating metal from the bright nickel layer. As stated, the plating metal may be nickel or a nickel-cobalt alloy which are deposited from relatively high temperature baths requiring stable mandrels such as the mandrels of the present invention.
An additional advantage of the present invention accruing from the flexibility of choice of materials for the solid model is ease of incorporation of division lines in
the final plated metal shell deposited on the mandrel. Grooves defining the location of such division lines may be easily formed in the shaped surface of the model. The copper layer conforms to these grooves of course, and when the composite mandrel is separated from the model, the grooves in the model surface create corresponding ridges on the copper plating surface of the mandrel. These ridges may be masked with electrically non-conductive tape or paint, so that when the mandrel is used in the intended electrodeposition process no deposition of plating metal takes place on those ridges. The final electrodeposited plating metal shell therefore is formed with edges defined by the position of the ridges, allowing separation of a desired part of the deposited shell for use as the final tool.
Aspects of the invention include electrodeposition apparatus including a cathode body formed as a composite mandrel of the kind formed by the method of the invention, described above. Such apparatus includes an anode body comprising plating metal, a cathode body having at least one exposed surface region for receiving build-up of plating metal by electrodeposition, an electrolyte solution comprising a salt of the plating metal, and means for passing current between the anode and cathode bodies via the electrolyte solution, CHARACTERISED IN THAT the cathode body comprises at least one shaped layer in the form of a copper shell one surface of which is bonded directly or indirectly to a backing mass, the other surface being at least partly exposed to the electrolyte solution, such exposed region (s) constituting the surface region (s) for receiving build up of plating metal.
In one aspect of the invention the cathode body of such apparatus comprises a mandrel with two electrodeposited copper layers to spaced from each other by the solid backing mass, and spacing posts may extend through the backing mass between opposed non-plating faces of the shells.
The invention will now be illustrated by reference to the following drawings, wherein: Figure 1 is a diagrammatic perspective view of a model body having a shaped upper surface.
Figure 2 is a cross sectional view of the model body of Figure 1 through A-A'.
Figure 3 shows the cross sectional view of the model body of Figure 1 with a copper layer electrodeposited on the shaped surface of the model and with keying elements glued to the exposed surface of the copper layer.
Figure 4 shows the model body of Figure 3, with shuttering erected to contain a backing mass cast against the exposed surface of the copper layer.
Figure 5 shows the composite mandrel formed by removal of the shuttering from Figure 4 and separation of the model body from the mandrel Figure 6 shows a diagrammatic cross sectional view of a double sided mandrel formed by casting a backing mass between two spaced model bodies formed in the same manner as the model body of Figures 1-4.
Figure 7 shows the double-sided mandrel of Figure 6 after separation of shuttering and model bodies.
Referring first to Figs. 1 and 2 a model body 1 of foamed polyurethane has a generally planar upper surface 2, on which two shape features are defined, namely a recess 3 and a protuberance 4. That surface has been shaped as the substantial reverse image of an intended plating surface of a mandrel for use in an electrodeposition process. CAD design equipment has been used to design and store the shape of the surface of the model body, and compatible associated
milling equipment has been used to mill the shape from a foamed polyurethane board material.
In Fig. 3, an electrodeposited copper layer 5 has been formed on the shaped surface of the mandrel, after activating that surface by application of a silver- containing paint. The copper layer 5 will ultimately form part of the intended mandrel for electrodeposition, the lower face of the layer which is in contact with the model body shaped surface 2 being the intended plating surface. On the upper exposed non-plating surface of the copper layer, irregularly shaped stone aggregate keying elements 6 have been randomly distributed and glued firmly to the surface by epoxy resin.
In Fig. 4, shuttering 7 has been erected around the model body 1. A backing mass 8 of DSP cement-and silica fume-based material, such as that marketed under the trade mark DENSITO by Densit A/S, Aalborg, Denmark, 1.5% by volume of steel fibres of diameter 0.4 mm and length 12.5 mm having been incorporated in the mass, has been cast against the non plating surface of the copper layer 5, and allowed to solidify. The stone aggregate keying elements 6 key the shell 5 into the backing mass 8.
In Fig. 5, the shuttering 7 has been removed and the polyurethane model body has been separated from the plating surface 10 of the copper layer 5 backed by backing mass 8. The composite of layer 5 and backing mass 8, generally indicated as 9, is the intended mandrel for electrodeposition of plating metal on the plating surface 10. The layer 5 being tightly keyed to the massive backing mass 8, the composite mandrel 9 is very strong and stable. Prior to use, the plating surface 10 of the mandrel may be worked by polishing or otherwise to remove any remnants of the model body or silver paint left adhering to the layer after separation of the mandrel from the model. The plating surface may also be worked to some extent to repair or fine tune the tolerances of key dimensions thereof. The composite mandrel of copper layer and DSP backing mass has CTE
properties not dissimilar from that of the usual plating metals, such as nickel and nickel/cobalt alloys. Hence the problem of differential expansion of plating metal layer and mandrel is reduced or eliminated. The DSP backing mass may be rendered substantially resistant to acid and chemical degradation in the plating bath by masking vulnerable surfaces with masking tape or by applying a resistant coating.
Referring now to Figure 6, an assembly of two model bodies, 1 and 11 is shown.
The model body 1 is that shown in Fig 3, with the copper layer 5 formed on the shaped surface 2 of the model body, and with stone aggregate keying elements 6 randomly distributed and glued to the non plating surface of the copper layer 5.
Again the surface of the copper layer in contact with the model body 1 is an intended plating surface of the intended double-sided mandrel. Model body 11 also has a differently shaped surface 22, onto which a second copper layer 15 has been formed, also with stone aggregate keying elements 16 randomly distributed and glued to its non plating surface. Model bodies 1 and 11 are arranged in spaced relationship, with opposed copper surfaces. Shuttering 17 is erected around the assembly and a backing mass 8 of DSP material is cast against the non plating surfaces, between the model bodies, and allowed to harden.
Not shown in Fig. 6 are optional spacing posts which may be fixed perpendicular to the opposed copper faces of the shells 5 and 15 and extending therebetween.
Such spacing posts are useful for maintaining the desired spacing distances between the two copper layers during casting of the backing mass.
In Figure 7 the shuttering 17 has been removed from the assembly of Fig. 6, and the polyurethane model bodies 1 and 11 separated from their respective copper layers 5 and 15.. The composite of layers 5 and 15 and backing mass 8, generally indicated as 19, is the intended double faced mandrel for electrodeposition of plating metal on the plating surfaces 10 and 20. Corrective milling of the plating surfaces and treatment to render them electrically conductive is as described in relation to the mandrel 9 of Fig 5.